October 13, 1905.] 



SCIENCE. 



457 



use is made of acid artificial manures. 

 That many soils containing naturally only 

 a trace of calcium carbonate remain fairly 

 fertile under ordinary farming conditions 

 is due, on the one hand, to ^n action of the 

 plant itself, which restores to the soil a 

 large proportion of the bases of the neutral 

 salts upon which it feeds, and partly to the 

 action of certain bacteria in the soil, which 

 ferment organic salts like calcium oxalate 

 existing in plant residues down to the state 

 of carbonate. Were it not for these two 

 agencies restoring bases the soil must nat- 

 urally lose its neutral reaction, since the 

 process of nitrification is continuously 

 withdrawing some base to combine with the 

 nitric and nitrous acids it sets free. 



This varying distribution of calcium 

 carbonate in soils suggests another section 

 of my subject, in which great activity has 

 prevailed of late— the undertaking of a 

 systematic series of soil analyses in any dis- 

 trict, with a view to making soil maps that 

 shall be of service to the agriculturist. 

 The Prussian government has long been 

 executing such a soil survey, and during 

 the last few years a similar project has 

 been pushed forward with great energy in 

 the United States; in France and in Bel- 

 gium several surveys are in progress, but 

 in the United Kingdom the matter has so 

 far only excited one or two local attempts. 

 While the basis of such work must always 

 be the geological survey of the district, 

 a geological survey in which, however, 

 the thin 'drift' formations are of greater 

 importance than the solid geology, there 

 are certain other items of information re- 

 quired by the farmer which would have to 

 be supplied by the agricultural specialist. 

 In the first place, the farmer wants to be 

 told the thickness of the superficial de- 

 posits; he requires frequent 'ground pro- 

 files, ' so that he can construct an imaginary 

 section through the upper 10 feet or so of 

 his ground. To take a concrete example: 



the chalk in the south of England is very 

 often overlaid by deposits of loam, ap- 

 proaching the nature of brick earth, and 

 the agricultural character of the land, its 

 suitability for some of the special crops, 

 like hops and fruit, which characterize that 

 district, will be wholly different according 

 as the deposit is 3 feet or 10 feet deep. 

 The proximity and, if near the surface, the 

 direction of flow of the ground water are 

 also matters on which there could be given 

 to the farmer information of great impor- 

 tance when questions of drainage or water- 

 supply have to be considered. It is neces- 

 sary also to refine upon the rough classifi- 

 cation of the soil and subsoil which alone 

 is possible to the field surveyor, one of 

 whose functions will be to procure typical 

 samples of which the texture and physical 

 structure can afterwards be worked out in 

 the laboratory. Geological formations are 

 constantly showing lithological changes as 

 one passes along their outcrop either in a 

 vertical sense or in their lateral extension ; 

 and these changes are often reflected by 

 corresponding changes in the character of 

 the soil which are of commercial impor- 

 tance. 



But while the mechanical analysis of the 

 soil has been of late the basis upon which 

 all soil surveys are constructed, it is of 

 equal importance, at any rate in the older 

 countries under intensive cultivation, to 

 undertake certain chemical determinations, 

 which come to possess a new value when 

 taken in connection with a soil survey. It 

 has been generally demonstrated that an 

 analysis, physical and chemical alike, of 

 the soil of a particular field, taken by itself, 

 possesses but little value. The physical 

 analysis will indicate roughly the character 

 of the soil, but very little better than could 

 have been learned by walking over the soil 

 and digging in it for five minutes; the 

 chemical analysis will disclose any glaring 

 deficiencies; but, as a rule, the analytical 



